Skeletal populations from the western coast of North America clearly were afflicted with a treponemal disease very different from that previously documented elsewhere in North America. Six populations from west of the Sierra Cascades were compared with 5 sites east of the Cascades. A high population frequency (both in adults and subadults) of pauci-ostotic, periostitis was noted in the six western skeletal populations, identical to that reported previously with bejel in Negev Bedouins, Sudanese Nubians, and the Kit site from Iraq. Early populations, from east of the Cascades, had a very different polyostotic disease pattern, characteristic of yaws, and identical to that previously reported in Guam. Both patterns were clearly distinguished from syphilis, which appears to be a later development (mutation?). This study provides evidence that the treponematoses were transported to the New World by way of at least two migrations, one bringing yaws; the other, bejel. The population with bejel likely derived from a different population than that with yaws. Given the absence of treponemal disease variation in the very wide spectrum of environments represented by the bejel-afflicted populations, it is clear that environment is not the factor determining disease character. This study expands on animal studies documenting that the individual treponematoses are separate diseases and not simply climate-induced variation